The Hydrogeomorphic (HGM) Approach for assessing wetlands was developed by the U.S. Army Corps of Engineers as a procedure for measuring the capacity of a wetland to perform functions. The Approach requires classification of wetlands based on geomorphic setting, water source, and hydrodynamics. For each wetland type, or subclass, it also requires developing models for each classified wetland, collecting data from reference wetlands, and calibrating the models using that data. The calibrated models are then field tested, revised, and published as a regional guidebook. The HGM Approach provides a tool to assess wetland functions, compute potential project impacts, calculate mitigation requirements, and project future with and without potential project conditions. Basic concepts for the HGM Approach were published in 1995, but implementation of the concepts to prepare regional guidebooks was initiated the previous year. It quickly became apparent that conversion from concepts to reality would require more detailed instructions and guidance. The objective of the Guidelines for Regional Guidebook Development is to provide that detailed guidance. These Guidelines contain detailed information on the background and overview of the HGM Approach; specific information on wetland classification; guidance on selecting reference wetlands, developing assessment models, collecting data from reference wetlands, and using that data to calibrate, verify field test, and validate the assessment models; and examples of potential application of model results to determine project impacts, mitigation requirements, and projections of futures with and without project conditions. Chapter 1 of the Guidelines for Regional Guidebook Development contains an overview and introduction to the HGM Approach and a general description of each of the nine tasks necessary to prepare regional guidebooks specific for particular wetland types.

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